Catalytic coated particulate filters

One of the most urgent goals of environmental policy – in addition to the reduction of environmentally harmful gaseous compounds – is the global reduction of particulate matter.

Soot particulates are emitted especially during combustion processes in diesel engines as well as the combustion of heavy fuel oils as in marine applications. The aim is to reduce the particulate mass (PM) but also the particulate number (PN) to avoid risks for the human health. A particulate filter removes particulate matter like soot or other unburned hydrocarbons (HC) from the exhaust gas by physical filtration or oxidation. The most efficient type is the so-called wall-flow filter. These substrates are similar to honeycomb structured substrates for common emission catalysts but blocked at alternative ends.

Therefore, the exhaust gas is forced to pass the porous walls between the channels and the particulate matter is deposited on the walls.

Since a continuous stream of soot would block the filter after a certain time, the filter has to be regenerated by burning off the filtered soot. Depending on the application and the regeneration strategy, the filter substrates are coated with specific catalytically active components in order to reduce the needed burn-off temperature or accelerate the oxidation of the filtered soot.

Once the pores of the filter are blocked, the backpressure of the exhaust system increases, and it has to be regenerated. This can be realized by a continuous process (passive regeneration) where nitrogen dioxide (NO2) is generated using nitrogen oxide (NO) from the exhaust gas in order to oxidize the soot. This method is called continuously regeneration trap (CRT®) and requires a minimum temperature of approximately 270 °C and a specific nitrogen oxide to soot ratio. If the exhaust gas conditions are not suitable for a passive regeneration system, an active regeneration can be performed, in which the temperature is raised above 450 °C (coated DPF) in order to burn off the soot in the presence of oxygen.

For a non-catalyzed filter, the soot oxidation will only start above 600 °C and will take a longer time compared to the coated type.

In addition to the regeneration capabilities, backpressure and catalyst activity are key issues.

INTERKAT is using a nanotechnology-based method for the coating of the filters. This always leads to highly active and homogeneous catalytic coating and a significantly lower pressure drop compared to standard coatings with washcoat.

INTERKAT also developed precious metal free coatings for filters which could be tailored for low regeneration temperature or high sulphur tolerance. The high sulphur tolerance of our base metal oxide coated filters is the key reason INTERKAT diesel particulate filters are widely used in large diesel engines e.g. for rail or marine applications.

“INTERKAT will always provide the optimal catalyst for your application”